Mechanical change gear transmissions including synchronized and non-synchronized multiple-speed transmissions for heavy-duty vehicles are well known in the prior art as may be seen by reference to U.S. Pat. Nos. 3,105,395; 4,735,109; 4,754,665; 5,086,897; 5,193,410, and 5,370,013, the disclosures of which are incorporated herein by reference. Such transmissions typically utilize an appropriate fluid to provide lubrication and cooling of rotating gears and shafts. Splash lubrication is provided by maintaining a sufficient level of fluid within the transmission sump so that various components rotate through the fluid and distribute it about the transmission. While splash lubrication provides a relatively simple and effective system for lubricating and cooling the transmission, some loss in efficiency results from the hydrodynamic drag induced by the components which rotate through the viscous lubricating fluid.
For applications which require additional lubrication and/or cooling, a forced lubrication system may be used in conjunction with an oil cooler or other supplemental heat exchanger. A number of such systems are known in the prior art as may be seen by reference to U.S. Pat. Nos. 4,356,889; 5,157,963, and 5,279,391, the disclosures of which are hereby incorporated by reference. These systems typically require an additional transmission-driven pump to circulate the transmission fluid throughout the lubrication and/or cooling circuit (s) which again results in some loss in efficiency.
Integrated powertrains which combine an engine and transmission into a unitized or multi-chamber housing have been developed as may be seen by reference to U.S. Pat. Nos. 3,642,097 and 5,467,668. However, these systems require substantial modifications to both the engine and transmission which must be made at the time of design and manufacture.